New-Build Window Regulations Explained

What Regulations Apply to New-Build Windows?

A builder who wants to know about New Build Building Regulations has a lot to consider:

They need to know:

“What do I actually need to order for this new house?”

The answer can involve several requirements simultaneously.

New-build windows and doors may need to address:

  • Part L – Energy efficiency
  • Part F – Ventilation
  • Part Q – Security
  • Part O – Overheating
  • Part B – Fire safety
  • Part K – Falling, collision and impact
  • Other accessibility/project requirements where applicable

Approved Documents provide government guidance on ways of meeting the Building Regulations; they are not themselves a substitute for assessing the actual project.

Rule Number One: Don’t Order From the Window Schedule Alone

An architect’s window schedule might show:

  • Window size
  • Opening style
  • Colour
  • Material

That does not necessarily contain the whole performance specification.

Before ordering, also obtain:

  • Energy/SAP information
  • Ventilation schedule
  • Overheating assessment
  • Security specification
  • Fire strategy
  • Glass specification

Otherwise the windows can be dimensionally correct and still technically wrong.

Part L – Thermal Performance

Part L covers energy efficiency.

The window specification may include a required whole-window Uw value.

Do not substitute a centre-pane Ug value.

As of August 2026, a new 2026 Approved Document L has been published for the Future Homes and Buildings Standards, but the amendment regulations take effect from 24 March 2027, subject to transitional provisions. Earlier Approved Document L versions continue to apply to projects subject to previous regulatory standards.

Therefore:

Do not put one universal new-build U-value on every quotation.

Ask which standard and energy specification applies.

Part F – Ventilation

New dwellings need a designed ventilation strategy.

This may involve:

  • Natural ventilation
  • Background ventilators
  • Mechanical extract
  • Continuous mechanical ventilation
  • MVHR

Don’t automatically add or remove trickle vents without checking the ventilation design.

The 2026 Approved Document F similarly applies to buildings subject to the 2026 standards, while earlier versions remain applicable to previous standards.

Part Q – Security

Part Q applies to new dwellings, including dwellings created by material change of use, and requires relevant doors and windows to resist unauthorised access.

PAS 24 is consequently a major procurement consideration.

Don’t ask merely:

“Is this system PAS 24?”

Ask:

“Is this exact size and configuration covered by the appropriate PAS 24 evidence?”

Part O – Overheating

Part O applies to new residential buildings.

This is particularly important where houses include:

  • Large bifolds
  • Sliding doors
  • Rooflights
  • Glazed gables
  • Large south/west elevations

The overheating assessment may specify a maximum glass g-value.

Do not order glass before checking it.

Part B – Fire Safety

Some windows may form part of:

  • Emergency escape arrangements
  • Fire-resistant construction
  • Compartmentation
  • Other aspects of the fire strategy

Where emergency escape windows are used under the relevant Approved Document B guidance, there are specific clear-opening requirements.

Never assume a standard opening sash automatically provides sufficient escape area.

Part K – Safety Glazing and Falling

Part K can affect:

  • Low-level glazing
  • Door glazing
  • Sidelights
  • Full-height windows
  • Protection against falling
  • Manifestation

Approved Document K contains the principal guidance on protection from falling, collision and impact.

The New-Build Specification Matrix

Before manufacture, every window should effectively be checked against these questions:

Thermal: What Uw is required?

Solar: Is there a maximum g-value?

Ventilation: What ventilation system is being used?

Security: Is PAS 24 required for this element?

Safety: Is the glazing in a critical impact location?

Fire: Does it provide escape or fire resistance?

Acoustic: Is an Rw/Rw+Ctr target specified?

Access: Are opening/threshold requirements specified?

Large Sliding Doors

Large sliders deserve special attention because they can trigger several requirements simultaneously:

  • Low Uw
  • Low g-value
  • Safety glass
  • PAS 24
  • Very high glass weights
  • Part O considerations

A slider should not simply be quoted as:

“4-panel aluminium patio door, 28mm glass.”

That isn’t a technical specification.

Bifold Doors

Check:

  • PAS 24 evidence
  • Panel sizes
  • Glass weight
  • Safety glazing
  • U-value
  • G-value
  • Threshold
  • Opening arrangement

Don’t assume every configuration in a product brochure is covered by the same performance evidence.

Window Restrictors

Restrictors can interact with:

  • Part K
  • Part B
  • Part O

If a window needs both child/fall protection and escape or overheating ventilation, select the hardware accordingly.

Documentation

Create a technical file containing, as applicable:

  • Uw calculations
  • WER documentation
  • Glass specifications
  • PAS 24 evidence
  • Ventilation schedule
  • Fire classifications
  • Product declarations
  • Installation instructions
  • Photographs

It is far easier to collect this during procurement than six months later.

Common New-Build Mistakes

Ordering before SAP/energy specification

Potentially expensive.

Treating every elevation the same

Part O may result in different solar-control specifications.

Using ordinary glass in PAS 24 configurations

Check the tested evidence.

Missing trickle vents

Or equally, adding vents blindly to an MVHR project.

Wrong escape hardware

Frame size alone doesn’t demonstrate escape performance.

Missing safety glazing

Particularly around doors and low levels.

Real-World Example

A developer needs windows for ten new houses.

The window schedule gives:

  • Sizes
  • RAL colour
  • Opening configurations

The supplier prices immediately.

Later the contractor discovers:

  • Uw target differs from the basic system
  • PAS 24 is required
  • West elevations require lower-g-value glass
  • Several bedrooms require escape configurations
  • Some windows require safety glazing
  • Ventilation strategy requires particular background ventilation

The original quotation is almost worthless.

A better procurement process gathers the technical specification first.

Frequently Asked Questions

Do all new-build windows need PAS 24?

Part Q security requirements apply to relevant accessible doors and windows; confirm the project-specific security specification and product evidence.

Do all new-build windows need trickle vents?

No universal answer. Follow the ventilation strategy.

Does Part O apply?

Yes, to new residential buildings.

What U-value do I need?

Use the applicable regulatory regime and project’s energy specification rather than assuming one figure applies universally.

Do windows need safety glass?

Where glazing falls into applicable critical locations or other safety requirements, appropriate safety measures are required.

Related Guides

  • Part L Explained
  • Part F Explained
  • Part Q Explained
  • Part O Explained
  • Part B Explained
  • Part K Explained
  • PAS 24 Explained
  • Window U-Values Explained
  • G-Values Explained
  • Building Control Checklist

Trade Tech Technical Support

For new-build pricing, send Trade Tech:

  • Architectural window schedule
  • Energy/SAP specification
  • Ventilation schedule
  • Part O/overheating requirements
  • Security specification
  • Fire strategy
  • Acoustic specification

That allows the quotation to be technically meaningful from day one.

Important: New-build compliance is project-specific. Never use a generic website article as a substitute for the project’s Approved Documents, Building Control requirements, energy assessment, fire strategy or certified product data.